JP5707435B2 - Noise filter - Google Patents

Description

  The present invention relates to a noise filter including two capacitors.

  For example, some power converters that boost or lower DC voltage include a noise filter for removing noise current (see Patent Document 1 below). The noise filter is connected to the input terminal and output terminal of the power converter, removes the noise current transmitted from the external device to the power converter via the input terminal, or generates the output terminal from the power converter. Noise current transmitted to external devices via The noise filter is composed of electronic components such as capacitors and coils and wirings for connecting these electronic components.

JP 2012-135175 A

  However, the noise filter may generate a new noise current from the capacitor and wiring connected to the capacitor. That is, the power conversion circuit has a portion where an alternating current flows, and an alternating magnetic field is generated around the alternating current. When an alternating magnetic field is linked to a capacitor, wiring, or the like, a new noise current (inductive noise current) is generated and goes out through an external terminal. Therefore, there is a demand for a noise filter in which a large induced noise current is less likely to be mixed into an external terminal even when an AC magnetic field is generated in a power conversion circuit.

  The present invention has been made in view of such a background, and an object thereof is to provide a noise filter in which a large induced noise current is difficult to be mixed into an external terminal.

One aspect of the present invention is a noise filter connected to an external terminal for electrically connecting a power conversion circuit to an external device,
Two capacitors,
With a metal housing connected to the ground,
The two capacitors are housed in the housing,
In the two capacitors, one electrode is electrically connected to the external terminal, and the other electrode is electrically connected to the housing.
A loop through which a current flows is formed by the two capacitors, the external terminal, and the housing.
In the loop, there are two regions, a first region and a second region, through which the magnetic flux of the alternating magnetic field generated from a part of the power conversion circuit penetrates, respectively.
When the magnetic flux passes through the first region, a first induced noise current is induced in the loop, and when the magnetic flux passes through the second region, the loop has a direction opposite to the first induced noise current. The noise filter is configured to induce a flowing second induced noise current (claim 1).

In the noise filter, the two capacitors, the external terminal, and the casing form the loop through which current flows. And it is comprised so that the magnetic flux of the alternating magnetic field generated from a part of power converter circuit may penetrate the above-mentioned two fields in a loop, respectively. When the magnetic flux passes through the first region, a first induced noise current is generated in the loop, and when the magnetic flux passes through the second region, a second induced noise current is generated in the loop. These two induced noise currents (first induced noise current and second induced noise current) are generated so as to flow in opposite directions in the loop.
Therefore, even if an induced noise current is generated in the loop, the two induced noise currents flow in opposite directions to each other and cancel each other and weaken. Therefore, it is difficult for a large induced noise current to be mixed into the external terminal.

  As described above, according to the present invention, it is possible to provide a noise filter in which a large induced noise current is difficult to be mixed into an external terminal.

The top view of the power converter device in Example 1. FIG. The principal part enlarged view of FIG. III-III sectional drawing of FIG. The figure for demonstrating the relationship between an alternating current magnetic field and an induction noise current in Example 1. FIG. VV sectional drawing of FIG. The top view of a housing | casing and a diode module in Example 1. FIG. VII-VII sectional drawing of FIG. VIII-VIII sectional drawing of FIG. The circuit diagram of the power converter device in Example 1. FIG. The principal part enlarged view of the power converter device in Example 2. FIG. XI-XI sectional drawing of FIG. The top view of the power converter device in Example 3. FIG. The conceptual diagram of the signal terminal in Example 4. FIG. The top view of the power converter device in Example 5. FIG. The top view of the power converter device in Example 6. FIG. The top view of the power converter device in Example 7. FIG. The top view of the power converter device in Example 8. FIG.

  Examples of the generation source of the AC magnetic field include an output terminal of a diode module in a power conversion circuit, a choke coil, and a transformer.

  The power conversion circuit can be, for example, a step-down circuit that steps down the voltage of a high-voltage DC power supply. And it can comprise so that a low voltage | pressure DC power supply may be charged using the reduced DC voltage.

Moreover, it is preferable that the current ratio, which is the ratio of the magnitudes of the first induced noise current and the second induced noise current, is 0.8 to 1.2.
In this case, since the two induced noise currents flowing in opposite directions are substantially the same, the remaining induced noise current after the two induced noise currents cancel each other can be reduced. . Therefore, the induction noise current mixed in the external terminal can be reduced.

The current ratio is preferably 0.9 to 1.1.
In this case, the induced noise current mixed in the external terminal can be further reduced.

Preferably, the electrodes of each of the capacitors are connected to a conductive wire, and the capacitor is electrically connected to the external terminal and the casing via the conductive wire.
In this case, the area of the loop can be increased by the conducting wire. For this reason, the magnetic flux of the alternating magnetic field easily penetrates the two regions in the loop. Therefore, two induced noise currents flowing in opposite directions are likely to be generated in the loop, and these two induced noise currents are easily canceled and weakened.

Further, the two capacitors are fixed to a printed circuit board, two metal support columns project from the bottom surface of the housing in the normal direction of the bottom surface, and the printed circuit board is supported by the support columns, and It is preferable that the support column is a part of the loop.
In this case, the area of the loop can be increased by the support. For this reason, the magnetic flux of the alternating magnetic field easily penetrates the two regions in the loop. Therefore, two induced noise currents flowing in opposite directions are likely to be generated in the loop, and these two induced noise currents are easily canceled and weakened.
Further, when the capacitor is fixed to the printed board as described above, the capacitor can be easily electrically connected to the external terminal or the housing using the wiring formed on the printed board.
Further, in the above configuration, since the loop is configured using the support for supporting the printed circuit board, it is not necessary to separate the support for supporting the printed circuit board and the support for forming the loop. Therefore, the number of support columns can be reduced, and the structure of the housing can be simplified.

Also, the alternating current that is the source of the alternating magnetic field flows in the normal direction, and when viewed from the normal direction, the two support columns from the alternating magnetic field generation unit that is the portion through which the alternating current flows. It is preferable that the distance to each other is equal (claim 6).
In this case, it becomes easy to generate two induced noise currents flowing in opposite directions in the loop. That is, since the alternating current flows in the normal direction, the alternating magnetic field has a cylindrical shape centered on the alternating current flowing in the normal direction. Therefore, the magnetic flux easily penetrates the two areas in the loop. In addition, when viewed from the normal direction, the distances from the AC magnetic field generation unit to the two support columns are equal to each other, so that the amount of magnetic flux that passes through the first region and the amount of magnetic flux that passes through the second region Can be made almost the same. Therefore, the intensity of the two induced noise currents can be made substantially the same, and the remaining induced noise currents after canceling each other can be weakened.

(Example 1)
Examples relating to the noise filter will be described with reference to FIGS. As shown in FIG. 1, the noise filter 1 of this example is connected to the external terminal 2 of the power conversion circuit 10. The noise filter 1 includes two capacitors 3 (3a, 3b) and a metal housing 4 connected to the ground. Two capacitors 3 are accommodated in a housing 4. As shown in FIGS. 2 and 3, the two capacitors 3 a and 3 b have one electrode 31 electrically connected to the external terminal 2 and the other electrode 32 electrically connected to the housing 4. Yes. As shown in FIG. 1, the housing 4 includes a bottom wall 40 and a side wall 49 erected from the bottom wall 40. Electronic components constituting the power conversion circuit 10 are fixed to the bottom wall 40. As shown in FIG. 3, a loop L through which a current flows is formed by the two capacitors 3 a and 3 b, the external terminal 2, and the housing 4.

  As shown in FIG. 3, in the loop L, the magnetic flux Φ of the AC magnetic field H generated from a part of the power conversion circuit 10 (AC magnetic field generation unit 7) penetrates, respectively, the first region S1, the second region S2, There are two areas. The first induction noise current I1 is induced in the loop L when the magnetic flux Φ passes through the first region S1. Further, when the magnetic flux Φ passes through the second region S2, a second induced noise current I2 that flows in the loop L in the opposite direction to the first induced noise current I1 is induced.

  The power conversion circuit 10 of this example is a step-down circuit (see FIG. 9). Using this step-down circuit, the DC voltage of the high-voltage DC power supply 8 is stepped down and the low-voltage DC power supply 80 is charged.

  As shown in FIG. 1, the power conversion device 11 includes an output terminal 2 a, an input terminal 2 b, and a signal terminal 2 c as the external terminals 2. In this example, the noise filter 1 is connected only to the output terminal 2a among these three external terminals 2 (2a to 2c).

  As shown in FIGS. 1 and 3, the capacitor 3 is fixed to the printed circuit board 14 in this example. The printed board 14 is supported by two metal columns 41 and 42. The support columns 41 and 42 protrude from the bottom surface 48 of the housing 4 in the normal direction (Z direction) of the bottom surface 48. The printed circuit board 14 is fixed to the columns 41 and 42 by bolts 5. The external terminal 2 is placed on the printed board 14.

  As shown in FIG. 2, one electrode 31 of the capacitors 3 a and 3 b is connected to the external terminal 2 via the wiring 6. The wiring 6 is a pattern formed on the surface of the printed board 14. Further, the other electrode 32 of the capacitor 3 is electrically connected to the columns 41 and 42 via the wiring 6 and the bolt 5. The wiring 6 extends linearly. The loop L is formed by the two capacitors 3 a and 3 b, the wiring 6, the external terminal 2, the bolt 5, the columns 41 and 42, and the housing 4.

The noise filter 1 of this example includes a filter coil 18 in addition to the capacitors 3a and 3b (see FIG. 9). The noise filter 1 of this example removes the conduction noise current generated in the power conversion circuit 10 so that the conduction noise current is not mixed into the output terminal 2a.
The filter coil 18 is configured by surrounding a part of the external terminal 2a with a filter core 180 made of a soft magnetic material.

  As shown in FIG. 2, in the vicinity of the noise filter 1, there is a portion (an AC magnetic field generator 7) where an AC magnetic field H is generated. In this example, an alternating magnetic field H is generated from an output terminal 151 of a diode module 15 described later.

  As shown in FIG. 3, an alternating current i flows in the Z direction at the output terminal 151 of the diode module 15. As shown in FIG. 2, the alternating magnetic field H has a cylindrical shape centered on the alternating current i flowing in the Z direction.

  Thus, since the magnetic flux Φ of the alternating magnetic field H is cylindrical, the magnetic flux Φ penetrates the two regions of the loop L (the first region S1 and the second region S2) as shown in FIGS. . As shown in FIG. 4, the magnetic flux Φ is generated in one of the two regions S1 and S2 from the near side IN, which is closer to the AC magnetic field generator 7 than the loop L, from the AC magnetic field generator than the loop L. It penetrates to the far side OUT which is the far side from 7. Further, the magnetic flux Φ penetrates the other region from the far side OUT to the near side IN. That is, the magnetic flux Φ always passes through the two regions S1 and S2 in opposite directions. Therefore, the first induction noise current I1 and the second induction noise current I2 generated in the loop L are opposite to each other.

That is, at a certain moment, the magnetic flux Φ passes through the loop L as shown in FIG. A component Φ _{x1 in} the X direction (projection direction of the external terminal 2) of the magnetic flux Φ ₁ passing through the first region S1 is directed from the far side OUT toward the near side IN. So as to prevent changes in the component [Phi _x1, the first inductive noise current I1 is generated in the loop L.

Further, the X-direction component Φ _x2 of the magnetic flux Φ ₂ penetrating the second region S2 is directed from the near side IN toward the far side OUT. So as to prevent changes in the component [Phi _x2, the second inductive noise current I2 is generated in the loop L.

Although AC magnetic field H orientation alternating, even in this way the direction is changed, the magnetic flux [Phi ₁ in the X direction component [Phi _x1, X-direction component [Phi _x2 flux [Phi ₂ is always facing away from each other. Therefore, the first induced noise current I1 and the second induced noise current I2 always flow in opposite directions. Therefore, the two induced noise currents I1 and I2 cancel each other.

  Moreover, as shown in FIG. 2, the conducting wire 6 of this example extends linearly in a direction (Y direction) orthogonal to both the X direction and the Z direction. When viewed from the Z direction, the distance r1 from the AC magnetic field generator 7 to the one bolt 5a is equal to the distance r2 from the AC magnetic field generator 7 to the other bolt 5b. In other words, the AC magnetic field generator 7 is located on the vertical bisector of the line connecting the two bolts 5a and 5b. As a result, the amount of magnetic flux Φ penetrating the two regions S1 and S2 is made equal, and the strengths of the two induced noise currents I1 and I2 induced in the loop L are made equal. Specifically, in this example, the current ratio I1 / I2, which is the ratio of the strengths of the two induction noise currents I1 and I2, is set to 0.8 to 1.2.

  As shown in FIG. 9, the power conversion circuit 10 of this example includes a MOS module 16, a transformer 13, a diode module 15, a choke coil 12, a smoothing capacitor 17, and a printed circuit board 14 (control circuit). The MOS module 16 is connected to the high-voltage DC power supply 8. The MOS module 16 incorporates four MOS elements 160. These four MOS elements 160 constitute an H bridge circuit.

  The output terminal of the MOS module 16 is connected to the primary coil 130 a of the transformer 13. This transformer 13 steps down the voltage of the high-voltage DC power supply 8. An output terminal 138 of the secondary coil 130 b of the transformer 13 is connected to the diode module 15. The center tap 139 of the transformer 13 is connected to the housing 4, that is, the ground.

  Two diodes 150 are provided in the diode module 15. The two diodes 150 are used to rectify the output voltage of the transformer 13. An output terminal 151 of the diode module 15 is connected to the choke coil 12. The output terminal 126 of the choke coil 12 is connected to the smoothing capacitor 17 and the filter coil 18. The choke coil 12 and the smoothing capacitor 17 are provided to smooth the waveform rectified by the diode module 15.

  As described above, in this example, the noise filter 1 is configured by the filter coil 18 and the two capacitors 3a and 3b. One electrode 31 of the capacitors 3 a and 3 b is connected to the external terminal 2 (output terminal 2 a), and the other electrode 32 is connected to the housing 4. Since the power conversion circuit 10 performs the switching operation of the MOS element 160, a conduction noise current is generated in the power conversion circuit 10 with this operation. The noise filter 1 is used to remove the conduction noise current so that it does not go outside through the output terminal 2a.

  On the other hand, as shown in FIGS. 5 and 7, in this example, the diode module 15 is placed on the bottom surface 48 of the housing 4, and the choke coil 12 is placed on the diode module 15. The choke coil 12 includes a core 121 made of a soft magnetic material and a winding portion 120 disposed in the core 121. As shown in FIG. 7, the input terminal 125 of the choke coil 12 protrudes from the winding portion 120 in the X direction, and the tip end portion 125 a is bent in the Z direction.

  As shown in FIGS. 6 and 7, the output terminal 151 of the diode module 15 protrudes from the sealing portion 159 in the X direction, and the tip portion 151 a is bent in the Z direction. As shown in FIG. 7, the tip 151a of the output terminal 151 of the diode module 15 and the tip 125a of the input terminal 125 of the choke coil 12 are overlapped and welded.

  Thus, since the output terminal 151 of the diode module 15 extends in the Z direction, the output current (alternating current i) of the diode module 15 flows in the Z direction. An alternating magnetic field H is generated around the output terminal 151.

  As shown in FIGS. 5 and 8, the output terminal 126 of the choke coil 12 extends from the winding portion 120 in the X direction. The external terminal 2 (output terminal 2a) is overlapped and welded to the output terminal 126.

The effect of this example will be described. In the noise filter 1 of this example, a loop L through which a current flows is formed by the two capacitors 3, the external terminal 2, and the housing 4. And the magnetic flux Φ of the alternating magnetic field H generated from a part of the power conversion circuit 10 is configured to pass through the two regions S1 and S2 in the loop L, respectively. The first induced noise current I1 is generated in the loop L when the magnetic flux Φ passes through the first region S1, and the second induced noise current I2 is generated in the loop L when the magnetic flux Φ passes through the second region S2. These two induction noise currents I1 and I2 are generated so as to flow in the loop L in opposite directions.
For this reason, even if an induction noise current is generated in the loop L, these two induction noise currents I1 and I2 flow in opposite directions to each other and cancel each other and weaken. Accordingly, it is difficult for a large induction noise current to be mixed into the external terminal 2.

In this example, the current ratio I1 / I2, which is the ratio of the strengths of the two induction noise currents I1 and I2, is 0.8 to 1.2.
Therefore, since the magnitudes of the two induced noise currents I1 and I2 flowing in opposite directions are substantially the same, the remaining induced noise current after the two induced noise currents I1 and I2 cancel each other is reduced. be able to. Therefore, the induced noise current mixed in the external terminal 2 can be reduced.

Further, as shown in FIG. 2, the electrodes 31 and 32 of the individual capacitors 3 a and 3 b are connected to the conducting wire 6. The capacitors 3 a and 3 b are electrically connected to the external terminal 2 and the housing 4 through the conductive wire 6.
Therefore, the area of the loop L can be increased by the conducting wire 6. Therefore, the magnetic flux Φ of the alternating magnetic field H can easily penetrate the two regions S1 and S2 in the loop L. Therefore, two induced noise currents I1 and I2 flowing in opposite directions are likely to be generated in the loop L, and these two induced noise currents I1 and I2 are easily canceled and weakened.

Further, as shown in FIG. 3, in this example, the columns 41 and 42 protruding from the bottom surface 48 of the housing 4 form a part of the loop L.
Therefore, the area of the loop L can be increased by the support columns 41 and 42. Therefore, the magnetic flux Φ of the alternating magnetic field H can easily penetrate the two regions S1 and S2 in the loop L. Therefore, two induced noise currents I1 and I2 flowing in opposite directions are likely to be generated in the loop L, and these two induced noise currents I1 and I2 are easily canceled and weakened.

  Further, as shown in FIG. 2, in this example, the capacitor 3 is fixed to the printed board 14. Therefore, the capacitor 3 can be easily electrically connected to the external terminal 2 and the housing 4 by using the conductive wire 6 patterned on the printed board.

  Further, in this example, as shown in FIG. 3, the loop L is configured by using support columns 41 and 42 for supporting the printed circuit board 14. Therefore, it is not necessary to separate the columns 41 and 42 for supporting the printed circuit board 14 and the columns for forming the loop L. Therefore, the number of support columns 41 and 42 can be reduced, and the structure of the housing 4 can be simplified.

  In this example, as shown in FIG. 3, the alternating current i that is the source of the alternating magnetic field H flows in the Z direction. Therefore, the alternating magnetic field H has a cylindrical shape centered on the alternating current i. Therefore, the magnetic flux Φ easily passes through the two regions S1 and S2 in the loop L. This makes it easy to generate two induced noise currents I1 and I2 that flow in opposite directions in the loop L.

  Further, in this example, as shown in FIG. 2, the distances r1 and r2 from the AC magnetic field generator 7 to the two columns 41 and 42 when viewed from the Z direction are made equal. Therefore, the amount of the magnetic flux Φ penetrating the first region S1 and the amount of the magnetic flux Φ penetrating the second region S2 can be made almost the same. Therefore, the intensity of the two induced noise currents I1 and I2 can be made substantially the same, and the remaining induced noise current after canceling each other can be weakened.

  As described above, according to this example, it is possible to provide a noise filter in which a large induced noise current is less likely to be mixed into an external terminal.

  The current ratio I1 / I2 may be 0.5 to 1.5, and if it is in the range of about 0.8 to 1.2, the induced noise current mixed in the external terminal 2 is substantially reduced. It can be reduced to such an extent that it does not become a problem. Ideally, the current ratio I1 / I2 is most desirably 1.0, but in actual implementation, the current ratio I1 / I2 is desirably 0.9 to 1.1.

  In this example, two capacitors 3a and 3b are used, but three or more capacitors 3 may be used. For example, another capacitor may be connected in parallel to each of the two capacitors 3a and 3b.

  In addition, each of the capacitor cells 3a and 3b can be configured using one capacitor cell, or can be configured using a plurality of capacitor cells.

(Example 2)
In this example, the structure of the loop L is changed. As shown in FIGS. 10 and 11, in this example, the lead wire 6 is not included in the loop L. In this example, one electrode 31 of the capacitors 3 a and 3 b is directly connected to the external terminal 2. Further, a metal connection member 140 is embedded in the printed circuit board 14, and the two columns 41 and 42 protruding from the bottom surface 48 of the housing 4 are in contact with the connection member 140. The other electrode 32 of the capacitors 3 a and 3 b is connected to the connection member 140. The capacitors 3a and 3b, the external terminal 2, the connection member 140, the support columns 41 and 42, and the housing 4 form a loop L through which current flows. Further, in this example, as shown in FIG. 10, there is an AC magnetic field generation unit 7 in the power conversion circuit 10, and the distances from the AC magnetic field generation unit 7 to the two capacitors 3a and 3b are equal to each other. Yes.

  In the loop L, there are two areas, a first area S1 and a second area S2. The magnetic flux Φ of the alternating magnetic field H passes through the two regions S1 and S2. As a result, two induced noise currents I1 and I2 flowing in opposite directions are generated in the loop L.

  Others are the same as in the first embodiment. Moreover, among the symbols used in the drawings relating to this example, the same symbols as those used in the first embodiment represent the same components as those in the first embodiment unless otherwise indicated.

(Example 3)
In this example, as shown in FIG. 12, two noise filters 1 are provided in the power converter 11. In this example, the first noise filter 1a is connected to the output terminal 2a, and the second noise filter 1b is connected to the input terminal 2b. In this example, the input terminal 2b is mounted on the printed circuit board 14, and two capacitors 3c and 3d are fixed to the printed circuit board 14. One electrode 31 of each of the capacitors 3c and 3d is connected to the input terminal 2b, and the other electrode 32 is connected to the housing 4 respectively. The capacitors 3c and 3d, the input terminal 2b, and the housing 4 form a loop L (second loop Lb) through which current flows.

  In this example, as in the first embodiment, a metal column (not shown) protrudes from the bottom surface 48 of the housing 4, and this column is electrically connected to the bolt 5. Further, the other electrode 32 of the capacitors 3 c and 3 d and the bolt 5 are connected via a conducting wire 6. One electrode 31 of the capacitors 3 c and 3 d and the input terminal 2 b are also connected via the conducting wire 6.

  The second noise filter 1b has a function of releasing a conduction noise current that enters the power conversion circuit 10 from the outside via the input terminal 2b to the ground (housing 4). An alternating magnetic field H is generated from the MOS module 16 located in the vicinity of the second noise filter 1b. The magnetic flux Φ of the alternating magnetic field H passes through the two regions S3 and S4 in the loop L, respectively. As a result, two induced noise currents I3 and I4 flowing in opposite directions are generated in the second loop Lb. The two induced noise currents I3 and I4 cancel each other and become weaker. Therefore, it is difficult for a large induced noise current to be output from the input terminal 2b.

  Others are the same as in the first embodiment. Moreover, among the symbols used in the drawings relating to this example, the same symbols as those used in the first embodiment represent the same components as those in the first embodiment unless otherwise indicated.

Example 4
In this example, the part where the noise filter 1 is formed is changed. As shown in FIG. 13, in this example, the noise filter 1 (third noise filter 1 c) is connected to the signal line 2 c of the printed circuit board 14. That is, one electrode 31 of the two capacitors 3 (3e, 3d) constituting the third noise filter 1c is connected to the signal line 2c, and the other electrode 32 is electrically connected to the housing 4 (not shown). . The two capacitors 3e and 3d, the signal line 2c, and the housing 4 form a loop L (third loop Lc) through which current flows.

  The signal line 2 c extends from the connector 140 of the printed board 14 into the printed board 14. The on / off operation of the MOS element 160 (see FIG. 9) is controlled by sending a control signal from the external device to the signal line 2c.

  The magnetic flux Φ of the AC magnetic field H passes through the two regions S5 and S6 in the third loop Lc. As a result, two induced noise currents I5 and I6 flowing in opposite directions are generated in the third loop Lc. The two induced noise currents I5 and I6 weaken each other. Therefore, a large induced noise current is not easily generated from the signal line 2c to the external device.

  Others are the same as in the first embodiment. Moreover, among the symbols used in the drawings relating to this example, the same symbols as those used in the first embodiment represent the same components as those in the first embodiment unless otherwise indicated.

(Example 5)
In this example, the shape of the choke coil 12 is changed. As shown in FIG. 14, the choke coil 12 of this example includes a winding part 120 and a core 121 that surrounds the winding part 120. The core 121 is made of a soft magnetic material. A part 129 of the winding part 120 is exposed from the core 121. An AC magnetic field H is generated from the exposed portion 129, and the magnetic flux Φ of the AC magnetic field H passes through the two regions S1 and S2 in the loop L.

  Of the winding portion 120 of the choke coil 12, a portion 129 exposed from the core 121 generates a particularly strong alternating magnetic field H. Even when such a strong AC magnetic field H is generated, a large induced noise current is unlikely to be mixed into the external terminal 2 in this example. That is, in this example, the magnetic flux Φ of the AC magnetic field H passes through the two regions S1 and S2 in the loop L, and two induced noise currents I1 and I2 that flow in opposite directions to the loop L are generated. It is. Therefore, even if a strong alternating magnetic field H is generated, the two induced noise currents I1 and I2 induced in the loop L can be canceled out, and the large induced noise current I can be prevented from being mixed into the external terminal 2.

  An alternating magnetic field H may be generated from the transformer 13. The transformer 13 includes a transformer winding part 130 (a primary coil 130 a and a secondary coil 130 b), and a transformer core 131 that surrounds the transformer winding part 130. A part 135 of the transformer winding part 130 is exposed from the transformer core 131. An AC magnetic field H may be generated from the exposed portion 135, and the magnetic flux Φ of the AC magnetic field H may pass through the two regions S1 and S2 in the loop L, respectively.

  A portion 135 of the transformer winding portion 130 exposed from the transformer core 131 generates a particularly strong alternating magnetic field H. Even when such a strong AC magnetic field H is generated, a large induced noise current is unlikely to be mixed into the external terminal 2 in this example. That is, in this example, the magnetic flux Φ of the AC magnetic field H passes through the two regions S1 and S2 in the loop L, and two induced noise currents I1 and I2 that flow in opposite directions to the loop L are generated. It is. Therefore, even if a strong alternating magnetic field H is generated, the two induced noise currents I1 and I2 induced in the loop L can be canceled out, and the large induced noise current I can be prevented from being mixed into the external terminal 2.

  Others are the same as in the first embodiment. Moreover, among the symbols used in the drawings relating to this example, the same symbols as those used in the first embodiment represent the same components as those in the first embodiment unless otherwise indicated.

(Example 6)
In this example, the structure of the capacitor 3 is changed. As shown in FIG. 15, the capacitors 3a and 3b of this example are constituted by two small capacitors 35 connected in series with each other. When two small capacitors 35 are connected in series in this way, even when one of the small capacitors 35 is short-circuited, the other small capacitor 35 can exhibit a normal function. Therefore, there is a merit that it is strong against failure. Alternatively, three or more small capacitors 35 may be connected in series to constitute individual capacitors 3a and 3b.

  Similarly, a plurality of small capacitors 35 may be connected in parallel to form individual capacitors 3a and 3b. In this case, since the overall capacitance of the capacitors 3a and 3b can be increased, the impedance can be reduced and a noise current can easily flow to the ground.

  Others are the same as in the first embodiment. Moreover, among the symbols used in the drawings relating to this example, the same symbols as those used in the first embodiment represent the same components as those in the first embodiment unless otherwise indicated.

(Example 7)
In this example, the structure of the capacitor 3 is changed. As shown in FIG. 16, in this example, a plurality of small capacitors 35 are connected in series to form small capacitor groups 300 and 301. The individual capacitors 3a and 3b are configured by connecting two small capacitor groups 300 and 301 in parallel. That is, one capacitor 3 includes a total of four small capacitors 35.

  If it does in this way, since the small capacitor | condenser 35 is connected in series, it becomes strong to a short circuit failure. In addition, since the small capacitor groups 300 and 301 are connected in parallel, the overall electrostatic capacity can be increased, and the noise current can easily flow to the ground.

  Others are the same as in the first embodiment. Moreover, among the symbols used in the drawings relating to this example, the same symbols as those used in the first embodiment represent the same components as those in the first embodiment unless otherwise indicated.

(Example 8)
In this example, the structure of the external terminal 2 is changed. As shown in FIG. 17, the external terminal 2 of this example has a first portion 28 and a second portion 29. The first portion 28 is provided in the housing 4, and the capacitors 3 a and 3 b are electrically connected to the first portion 28. An opening 450 is formed in the housing 4, and the second portion 29 is inserted through the opening 450. The first portion 28 and the second portion 29 are connected by a screw 27. Further, an external device is connected to the distal end portion 290 of the second portion 29.

  Others are the same as in the first embodiment. Moreover, among the symbols used in the drawings relating to this example, the same symbols as those used in the first embodiment represent the same components as those in the first embodiment unless otherwise indicated.

DESCRIPTION OF SYMBOLS 1 Noise filter 10 Power conversion circuit 2 External terminal 3 Capacitor 31 One electrode 32 The other electrode 4 Case I1 1st induction noise current I2 2nd induction noise current L loop S1 1st area | region S2 2nd area | region

Claims (6)

A noise filter (1) connected to an external terminal (2) for electrically connecting the power conversion circuit (10) to an external device,
Two capacitors (3a, 3b);
A metal casing (4) connected to the ground,
The two capacitors (3a, 3b) are accommodated in the casing (4),
In the two capacitors (3a, 3b), one electrode (31) is electrically connected to the external terminal (2), and the other electrode (32) is electrically connected to the housing (4). Connected to
The two capacitors (3a, 3b), the external terminal (2), and the housing (4) form a loop (L) through which current flows,
In the loop (L), there are two regions, a first region (S1) and a second region (S2), through which the magnetic flux of the alternating magnetic field generated from a part of the power conversion circuit (10) penetrates. ,
When the magnetic flux passes through the first region (S1), a first induction noise current (I1) is induced in the loop (L), and when the magnetic flux passes through the second region (S2), the loop ( A noise filter (1), wherein a second induced noise current (I2) flowing in a direction opposite to the first induced noise current (I1) is induced in L).   The noise filter (1) according to claim 1, wherein a current ratio (I1 / I2), which is a ratio of the magnitudes of the first induced noise current (I1) and the second induced noise current (I2), is 0. A noise filter (1) characterized by being 8 to 1.2.   The noise filter (1) according to claim 2, wherein the current ratio (I1 / I2) is 0.9 to 1.1.   In the noise filter (1) according to any one of claims 1 to 3, the electrodes (31, 32) of the individual capacitors (3a, 3b) are connected to a conductor (6), The noise filter (1), wherein the capacitor (3a, 3b) is electrically connected to the external terminal (2) and the housing (4) through the conductive wire (6).   The noise filter (1) according to any one of claims 1 to 4, wherein the two capacitors (3a, 3b) are fixed to a printed circuit board (14), and a bottom surface of the housing (4). Two metal posts (41, 42) project from (48) in the normal direction of the bottom surface (48), and the printed circuit board (14) is supported by the posts (41, 42), and The noise filter (1), wherein the support columns (41, 42) form a part of the loop (L).   The noise filter (1) according to claim 5, wherein an alternating current (i) that is a source of the alternating magnetic field flows in the normal direction, and when viewed from the normal direction, the alternating current ( The noise filter (1), wherein the distances (r1, r2) from the alternating magnetic field generator (7), which is a portion through which i) flows, to the two struts (41, 42) are equal to each other.

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